Spiraling                                                                                                                            

                                                                                                                


                                                                                                               
Why should a football quarterback throw a football with a spiral?                                 
hunter-ed.com

    Lots of kinetic energy in a thrown football is lost due to air drag. The force of air drag, which is in the opposite direction of motion, is given by ½C(rho)(v^2)A. The character we're interested in is A, the area. When the football is pointed in the direction it's moving, the ball will allow more flow, a small A. This results in less drag and thus can be thrown farther. In fact, when a football is thrown well, with a perfect spiral, it will only lose 41% of it's original kinetic energy if the football is thrown at pi/4 radians at 100ft/s. However, if a football is thrown to 'tumble' through the air, drag is a huge factor; 77% of the kinetic energy is lost if the ball is thrown at pi/4 radians at 100ft/s. The difference in energy loss forces quarterbacks to learn how to throw the football with a spiral. This concept is also applied to bullets. When a gun fires a bullet, the bullet spirals to the target because the less air drag will allow the bullet to go much further/faster than if it was not spiraling.

Do all football players use the spiral technique when passing the football?

    Sometimes, like for example during a kickoff, a kicker will purposefully kick the football to tumble 'head over heals' to the other side of the football field instead of using a spiral. The kicker does this to increase A. While the football is tumbling, the football will have significantly more air drag. This is done in an attempt to maximize air time to give his team more time to run down the field.

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